Problem: Solve for $x$ and $y$ using substitution. ${3x-y = 11}$ ${x = 3y-7}$
Explanation: Since $x$ has already been solved for, substitute $3y-7$ for $x$ in the first equation. ${3}{(3y-7)}{- y = 11}$ Simplify and solve for $y$ $9y-21 - y = 11$ $8y-21 = 11$ $8y-21{+21} = 11{+21}$ $8y = 32$ $\dfrac{8y}{{8}} = \dfrac{32}{{8}}$ ${y = 4}$ Now that you know ${y = 4}$ , plug it back into $\thinspace {x = 3y-7}\thinspace$ to find $x$ ${x = 3}{(4)}{ - 7}$ $x = 12 - 7$ ${x = 5}$ You can also plug ${y = 4}$ into $\thinspace {3x-y = 11}\thinspace$ and get the same answer for $x$ : ${3x - }{(4)}{= 11}$ ${x = 5}$